Importance of the vein of Marshall involvement in mitral isthmus ablation

Abstract

Background Epicardiac conduction via the vein of Marshall (VOM) can bypass the mitral isthmus (MI) line, making MI ablation difficult. This study aimed to assess the contribution of the VOM in achieving MI conduction block. Methods This study included 143 consecutive patients with nonparoxysmal atrial fibrillation who underwent initial MI ablation. They were retrospectively classified into two groups, a VOM‐guided group (n = 28) and a conventional group (n = 115), according to the use of a 2‐Fr electrode catheter inserted in the VOM. The acute success rate of achieving MI block and the ablation data were assessed. When the bidirectional block was verified exclusively in the VOM or coronary sinus (CS) electrodes, we defined it as a pseudo MI block. In the VOM‐guided group, we ascertained the complete MI block, verified both in the VOM and CS electrodes. Results In the VOM‐guided group, the pseudoblock was observed in 33.3% of the patients during MI ablation. With significantly less radiofrequency energy (19 322.6 ± 11 352.8 vs 25 389.3 ± 19 951.9, P = 0.04), we achieved a similar level of success rate in MI ablation in the VOM‐guided group (96.4% vs 91.3%, P = 0.36). Notably, after achieving complete MI block, atrial burst pacing induced two perimitral flutters in the VOM‐guided group, which were successfully terminated by the additional radiofrequency application. Conclusions Assessment of electrical conduction through the VOM could clarify the existence of a pseudo MI conduction block. However, the existence of a slow conduction through the MI could be detected only after induction of perimitral atrial tachycardia with atrial programmed stimulation.

The ligament of Marshall and arrhythmias: A review

“…Ablation targeting the insertion sites achieved mitral line block in 75% patients. Similar findings were also demonstrated by Fujisawa et al 25 who demonstrated that one‐third of the patients showed a pseudo‐block during mitral isthmus ablation that was verified both in the VOM and CS electrodes.…”

“…A recent study by Barrio‐Lopez et al 34 also reported a prevalence of 13.5% (72/534) for the presence of epicardial connections between PVs and other anatomic structures. As mentioned above, the LOM serves as not only an arrhythmogenic source of AF but also as a portion of re‐entry circuit for macro‐re‐entrant AT after AF ablation 20,22–26 . Epicardial ablation of LOM is a feasible and effective option, which does not appear to increase the complication risk.…”

Incidence, electrophysiological characteristics, and long-term follow-up of perimitral atrial flutter in patients with previously confirmed mitral isthmus block

“…This may create a selective block towards the CS multipolar catheter but not to the entire MI. Presumably, some cardiac bundles may remain intact, and as we have learned, these may be located in the myocardial coverage of the vein of Marshall, the complex anatomical region of the LA ridge, the lateral aspect of the LAA base, or the area between the LAA and the mitral annulus [18][19][20][21]. Apparently, the impulse is passing through the remaining MI connections with a very long delay.…”

“…This can lead to the persistence of conduction gaps that allow the maintenance of PMF despite the apparent evidence of complete block. This is a condition often referred to as MI pseudo-block [18][19][20][21].…”

Ligament of Marshall ablation for persistent atrial fibrillation

“…MI thickness and length may impact acute and long‐term success. The VOM bundle has more recently been identified as an important anatomical factor, and is protected from endocardial RF by adipose tissue insulation 14,15,57,58,71,72 . Several reports have shown its role in a substantial proportion of cases of MI reconnections, promoting additional RF in the CS lumen or left PV/LAA ridge during MI ablation (connecting areas of the VOM) 9,10,73 .…”